The book, from the point of view of the New Chronology, examines two of the most interesting and mysterious eras of Russian history - the reign of Ivan the Terrible and the reign of Peter the Great. Both eras are considered a turning point in Russian history, which significantly influenced the further development of the country. Both contain many mysteries and not fully understood events. The first part of the book is dedicated to the reign of Ivan the Terrible. The authors provide new details that confirm and complement the reconstruction of the reign of Ivan the Terrible, which they proposed in 1995, as a sequence of reigns of four different kings. The second part of the book is devoted to new facts discovered during the authors' research into the astronomical zodiac of Ivan the Terrible, depicted on the famous bone throne of Ivan the Terrible, stored in Armory Chamber of the Moscow Kremlin. Unexpectedly, it turned out that in the history of Peter I there was hidden a certain secret related to the CHANGE OF THE TSAR’S NAME. This most likely means that under the name of Peter the Great, a completely different person with a completely different name reigned on the Russian throne. That is, an IMPOSTER. Which explains a lot in Russian history. The book does not require special knowledge and is intended for anyone interested in using mathematics to uncover the mysteries of our history.